Many different electropolishing processes may be used for the processing of various metals and its alloy. The purpose of the process of electrochemical polishing or electropolishing is to produce metal surfaces of high purity, and to smooth and deburr the metal surfaces. Smoothing in the micro range can also produce gloss in the treated wafer surfaces. Furthermore, electropolishing can also remove any stresses from the outer layers of the metal layers.
The electroplating deposition (“ECD”) of copper is the main technology for through-silicon via (“TSV”) filling in advanced packaging. In the ECD process, rapid deposition of copper requires the prior formation of barrier and seed layers. Then, chemical mechanical polishing (“CMP”) is used to removing the copper overburden on the wafer. The redistribution layer is typically formed after these steps. Due to the high cost of CMP equipment and slurry consumption, one cannot significantly decreasing the cost of the total process that includes a CMP step.
The patent EP1382065 “Electropolishing metal layers on wafers having trenches or vias with dummy structure” appears to disclose an electropolishing technology in a dual-damascene process. The method of forming copper interconnect in the front end of line semiconductor procedure is presented. But the patent does not appear to address removing copper facets formed by electroplating, and does not suggest barrier layer reuse.
An appreciable obstacle to the removal of overburden copper facets is the difficulty of smoothing and deburring the metal layer surface in semiconductor manufacturing in recent years. This is due to the difficulty in volatilizing the compound formed during inductively coupled plasma (“ICP”) etching processes. CMP of such surfaces is rather expensive and may produce stress in the surface structure of the wafer, which can have an adverse effect on the corrosion resistance of the wafer. The barrier layer, instead of being recycled for use in the subsequent step, is removed in the CMP process. Accordingly, the CMP produces waste and may be harmful to the environment.
Electrochemical polishing of metal surfaces in semiconductor manufacturing is one alternative. U.S. Pat. No. 6,679,980B1 presents an electropolishing process that can be used for a metal and its alloy layer, which consists of cobalt-chromium-tungsten. As described in H. Surmann, “Automatiserter Entwurf von Fuzzy Systemen”, VDI Verlag (1995) Series 8, No. 452, the papers presented in this field concentrate primarily on special equipment and control systems of the electropolishing process.